There has been disclosed a single-crystal cutting method for cutting a single-crystal member having a cleavage plane along a planned cutting plane by allowing a machining tool that cuts the single-crystal member to cut into a single-crystal member while relatively moving the single-crystal member and the machining tool, providing a cutting direction of the machining tool in a direction inclined toward a direction along which chips of the single-crystal member are discharged by a cutting tool with respect to a normal direction vertical to an intersection line of the planned cutting plane and the cleavage plane, and providing an inclination angle of the cutting direction from the normal line as an angle at which cutting efficiency of the single-crystal member provided by the machining tool becomes maximal (see, e.g., Patent Document 1). According to this single-crystal cutting method, the cleavage plane of the single-crystal member appears as intersection lines A and B on the cutting planned plane. Further, the cutting direction along which the cutting efficiency becomes maximal is each of Z1, Z2, Z3, Z4, Z5, Z6, Z7, and Z8 directions inclined at rotation angles θ1, θ2, θ3, θ4, θ5, θ6, θ7, and θ8 toward a clockwise or counterclockwise chip discharge direction from normal lines P and Q vertical to respective intersection lines A and B. Furthermore, when the single-crystal member is made of lithium tantalite, θ1 is 24 degrees, θ2 is seven degrees, θ3 is 16 degrees, θ4 is 8 degrees, θ5 is 20 degrees, θ6 is 17 degrees, θ7 is 16 degrees, and θ8 is 5 degrees.
According to the thus configured single-crystal cutting method, the direction along which chips of the single-crystal member are discharge is determined as a positive rotation angle with respect to each normal line that is present on the planned cutting plane of the single crystal and vertical to each intersection line of this planned cutting plane and the cleavage plane, cutting is effected from the direction along which the cutting efficiency becomes maximal that is determined by crystallographic characteristics of the single-crystal member having this positive rotation angle and pressure contact force between this single-crystal member and the machining tool, the single-crystal member is then cut, and hence cutting elimination efficiency is greatly improved, thus shortening a long cutting machining time. Moreover, since excessive distortion is not applied to the single-crystal member during machining, a cut wafer does not bend or warp.
On the other hand, there is disclosed a single-crystal cutting method for slicing a single-crystal ingot along a planned cutting plane by allowing a cutter to cut into the single-crystal ingot while relatively moving the single-crystal ingot and the cutter, setting a crystal orientation of the single-crystal ingot to <111>, and effecting slicing in parallel with a direction of a crystal habit line (see, e.g., Patent Document 2).
According to the thus configured single-crystal cutting method, since <111> is determined as the crystal orientation of the single-crystal ingot in advance and the single-crystal ingot is sliced in parallel with a direction of the crystal habit line by the cutter in a state that a cutting direction of the cutter is set to the direction of the crystal habit line of the single-crystal ingot, a wafer that very hardly bends or warps can be cut and separated, and cutting machining efficiency can be considerably improved. That is, a cleavage plane of a macro single crystal ingot is usually a (111) plane, the slice direction of the single crystal ingot is corrected along the crystal habit line that is produced due to a difference in development level between crystal planes, and hence an ideal wafer that very hardly bends or warps can be obtained from the cut wafer.